The present invention relates to a drive control apparatus for controlling driving of a forklift.
Conventionally, forklifts are widely used as industrial vehicles for handling loads (picking up and placing of loads) in plants. Due to its characteristic usage, the driving stability of this type of forklift greatly varies depending on the load state. For example, the center of gravity of the vehicle is shifted and the driving stability varies between a state of carrying no loads and a state of carrying a load. When carrying a load, the driving stability varies depending on the weight of the load, the height of the fork on which the load is mounted, the tilt angle of the fork. Thus, conventionally, a technique for limiting the driving of a forklift to improve the driving stability of the vehicle is disclosed in Japanese Laid-Open Patent Publication Nos. 2001-31391 and 2000-179372. The technique disclosed in the publication No. 2001-31391 limits the vehicle speed in accordance with the load state of the forklift, so that the forklift always travels at an optimum safety speed. The publication No. 2000-179372 discloses an outdoor driving mode and an indoor driving mode. A speed limit is set for each of the outdoor and indoor driving modes, thereby limiting increase of the engine speed.
As described above, forklifts are industrial vehicles performing loading operations. In the case where the vehicle driving force is derived from the engine, most forklifts uses the power of the engine for actuating loading device as well as for driving the vehicle. Thus, since increase of the engine speed is suppressed so that the vehicle speed does not exceed the speed limit in a forklift that limits the driving of the vehicle (vehicle speed), loading operation (actuation of the loading device) needs to be performed with a lowered engine power while the speed is limited, which can degrade the efficiency of the loading operation. In this respect, the technique disclosed in the publication No. 2000-179372 cancels the limitation on the driving during the loading operation, thereby preventing the efficiency of the loading operation from being degraded. More specifically, in the publication No. 2000-179372, the driving mode with the speed limit is cancelled when an operation of a loading operation lever is detected, and is switched to a mode prioritizing the loading operation.
In the publication No. 2000-179372, the limitation on the driving is cancelled based only on the operation state of the loading operation lever. When the driver manipulates the loading operation lever in preparation for a loading operation, the limitation on the driving is cancelled. The cancellation of the limitation causes the engine speed to be increased in accordance with depression of the accelerator pedal. Therefore, the stability of the vehicle can be degraded by a sudden acceleration.